Field of the Invention
The present invention relates to a heat-shrinkable protective element and to its process of manufacture.
It applies typically but not exclusively to the fields of low-voltage (in particular of less than 6 kV), medium-voltage (in particular from 6 to 45-60 kV) or high-voltage (in particular greater than 60 kV and which can range up to 800 kV) energy cables and fittings, whether direct current or alternating current.
Description of Related Art
A heat-shrinkable protective element may be conventionally called “heatshrink” or “heat-shrink sleeve” in the field of cable manufacture.
A heatshrink is a sheath which shrinks in the radial direction with respect to the longitudinal axis of the cable, when it is heated above a certain temperature. Typically, the volume of the material constituting the heatshrink remains constant between the shrinkable or nonshrunken state and the shrunken state: the thickness of the shrunken sheath is thus greater than the thickness of the nonshrunken sheath. The degree of shrinkage of a heat shrink can be between 100 and 600%, the degree of shrinkage being the ratio of the internal diameter of the sheath in the nonshrunken state to the internal diameter of the sheath in the shrunken state (obtained after heat treatment).
As such, it is difficult to manufacture a heat-shrinkable protective element having electrical insulating properties, which becomes semiconducting in the shrunken state subsequent to its heat treatment, while guaranteeing good mechanical properties once the protective element has shrunk.